1. Field of the Invention
This invention generally relates to environment mapping and, more particularly, to a system and method for modifying a two-dimensional (2D) light detection and ranging (LiDAR) system for use in three-dimensional (3D) mapping.
2. Description of the Related Art
A LiDAR is often the primary source of sensor data used by robots for Simultaneous Localization And Mapping (SLAM) reconstruction, obstacle detection and avoidance, feature detection, and scene classification, as well as other applications in the field of mobile robotics. LiDAR uses ultraviolet, visible, or near infrared light to image objects. A fixed 2D LiDAR can be constructed by bouncing a laser beam off a spinning mirror. As with RADAR, the difference in time between transmitted and returned signals determines the distance to, and shape of objects in the environment. This is a functionally limited, but inexpensive and robust device. Fixed 2D LiDAR units are often configured to face forward. Forward-facing, 2D LiDARs sample a planar slice of the environment, and thus are not fully aware of their surroundings.
FIGS. 1A and 1B are, respectively, a plan (top) view of a 2D LiDAR at rest, and a horizontal beam sweep (prior art). In FIG. 1A the laser beam faces forward, along the X-axis. In FIG. 1B, an actuator sweeps the laser beam through a horizontally oriented 270° arc about the (vertical) Z-axis. Notice the “blind spot” behind the LiDAR. In theory, the horizontal sweep can cover a full 360 degrees, but in practice the sweep is usually limited by chassis supporting the laser and mirror. However, the main limitation is that the sweep only covers a narrow horizontal sliver of the environment.
FIG. 2 is a diagram of a conventional 2D LiDAR device (prior art). The laser reflected off the rotating mirror creates the horizontal sweep.
To improve upon this performance, 3D LiDAR products mechanically tilt (or “nod”) the basic 2D LiDAR or spin it freely about an axis that is in the plane of the 2D scan. The nodding design creates a longitudinal scan pattern with maximum sample density at the poles of the nodding axis. The fully rotating design can scan a more complete field of view, but it requires a complex mechanical linkage.
Because the laser is a power consuming device these configurations require some means to get power and data onto and off of the spinning LiDAR device. One solution to this problem is to use slip-ring electrical contacts that are subject to mechanical wear. Another solution is to co-locate batteries on the spinning LiDAR unit. But without a supplemental charging source the batteries run down, thus limiting service uptime. Both of these solutions come with increased maintenance requirements and introduce potential failure points.
It would be advantageous if conventional 2D LiDAR technology could be augmented to create 3D mapping scans and thus replace the vastly more expensive 3D LiDAR products that are on the market today.